Amine formation and metabolic activity of microorganisms in the ileum of young swine fed chlortetracycline.

The favorable effect of low levels of chlortetracycline (Aureomycin) in promoting an increased rate of gain in young swine is widely accepted as a contribution to our agricultural economy (Jukes, 1955). In young swine farrowed by hysterectomy and reared in isolation, with relative freedom from the more common infections to which baby pigs are exposed, significant increases in rate of growth occurred when their diets were supplemented with low levels (10 to 40 ppm) of chlortetracycline (Hill and Larson, 1955). In view of this result an attempt has been made to learn if there are detectable effects of chlortetracycline on organisms of the intestinal tract, in addition to suppression of those producing disease. Stokstad (1954) has stated that antibiotic effect in promoting increased growth apparently is confined to action on bacteria within the intestinal tract. Several investigators have reported experiences suggesting that chlortetracycline suppresses the formation of toxic substances such as amines in the intestinal tracts of young animals. Sieburth et al. (1954) found support for this contention when they observed that a marked dilation of the blood vessels of the small intestine, and a reduction of the pungency of odors of the intestinal contents, occurred in chicks whose feeds were supplemented with 10 ppm of chlortetracycline. Michel (1956) and Michel and Francois (1956) reported that the microflora of the intestinal contents of swine were very active in the decarboxylation of amino acids. Aspartic acid and glutamic acid were most readily decarboxylated; arginine, histidine, alanine, and tryptophan also were attacked; lysine, ornithine, and methionine were rarely affected. There was great variation from animal to animal. Decarboxylation of tryptophan was not consistently inhibited by chlortetracycline, but decarboxylation of aspartic acid, glutamic acid, and arginine was markedly reduced in the presence of chlortetracycline. Melnykovych and Johansson (1955) reported a reduction of amine formation in the gut of rats fed chlortetracycline. In studying the effect of tetracyclines on enzymatic activities of intestinal bacteria of rats, Melnykovych (1956) found that, although the decarboxylase activities of these organisms were not inhibited in the presence of suitable substrate and chlortetracycline, the adaptive formation of certain amino acid decarboxylases was prevented if tetracyclines were added to the medium before growth was initiated. Our recent experiments have been directed to chromatographic, electrophoretic, and manometric studies of ileum contents because bacteriological cultures of intestinal contents from young swine receiving chlortetracycline as a feed supplement showed a greater suppression of clostridia and enterococci in the ileum than in other portions of the intestinal tract (Larson and Hill, 1955).